Even this plot ends poorly (5)
I believe the answer is:
still
'even' is the definition.
(I know that even can be written as still)
'this plot ends poorly' is the wordplay.
'ends' indicates one should take the final letters.
'poorly' becomes 'ill' (synonyms).
The final letters of 'this plot' are 'st'.
'st'+'ill'='STILL'
(Other definitions for still that I've seen before include "source of spirits" , "... [STRONG LIQUOR] produced by this" , "Motionless, not sparkling" , "Immobile" , "inaudible" .)